Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardias that are frequently caused by the presence of an "arrhythmogenic region" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart. The heart includes a number of normal pathways that are responsible for the propagation of electrical signals from upper to lower chamber necessary for performing normal function. The presence of arrhythmogenic region or accessory pathways can bypass or short circuit the normal pathways, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Cardiac mapping is used to locate aberrant electrical pathways and currents emanating within the heart. The aberrant pathways cause the contractions of the heart muscle to take on abnormal and life threatening dysrhythmias. Intracardiac mapping requires careful positioning of a plurality of catheters of multiple electrodes within the heart. For example, Webster, Jr. in U.S. Pat. No. 4,960,134 shows the general use of a catheter. It is important for a catheter to move into and out of the heart chamber freely without any obstruction or potential complications of component disengagement from the catheter shaft.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying cause. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a clinician to be able to accurately steer the catheter to the region for ablation. Once at the region, it is important for a catheter to intimately contact the tissue to effectively control the emission of energy to ablate the tissue within the heart.
Regardless of the type of mapping means or ablation means used, the clinician is called upon to remotely move, rotate, push, pull, and manipulate the catheters in various ways. First, a catheter is inserted into a major vein or artery, usually in the neck or groin area. It is then guided into chambers of the heart by appropriate manipulation through the vein or artery. The distal section of a catheter must be manipulatable by a user from the proximal end of the catheter, so that the electrodes at the distal section can be positioned against the tissue at the desired location to assure that all aberrant electrical pathways are mapped and later ablated.
Development of prior electrode catheters has focused upon the requirements of electrical continuity and interference problems. However, the mechanical and safety considerations have been overlooked. In general, a conducting wire is soldered to the tip electrode or a band electrode. The electrode with a conducting wire is thereafter placed and secured onto the catheter shaft, mostly by gluing with an appropriate adhesive. The bonding force between a tip electrode and the catheter shaft is proportional to the contact surface area and is substantially maintained so long as the contact is intimate and intact. It has been reported that the tip electrode might sometimes disengage from the distal section of the catheter shaft. The frequency of tip electrode disengagement becomes more often as a result of thermal cycling to the catheter. This includes the cases of applying the RF energy to a tip electrode in ablation procedures or when the catheter is re-sterilized through high temperature cycles. In one instance, an electrode catheter can be made of PebaxTm material, which is polyether/amide block copolymer (supplied by Elf Atochem North America, Inc., Philadelphia, Pa.). Its coefficient of linear thermal expansion is reported as 220.times.10.sup.-6 inch/inch/.degree. C. For a catheter to endure an ablation temperature of up to 90.degree. C., the linear thermal expansion from the room temperature of 25.degree. C. is calculated as 1.4%. In other words, the plastic portion may expand by a factor of 1.4% when its temperature is increased from 25.degree. C. to 90.degree. C. Repetitive cycles of thermal expansion and contraction may lead to eventual failure of the bonding force between the catheter shaft and the tip electrode.
The electrode is generally prone to separating from its main catheter shaft body because of repetitive thermal cycling, resulting in separation of the catheter shaft from the stem of a tip electrode. The tip electrode might inadvertently be separated from the catheter shaft and be left behind in a patient's heart or in a circulation system, causing undesired health hazard.
The prior catheter development has overlooked the important need to provide a safe catheter system having safety means in association with the required bonding force. It is an objective of this invention to provide needed safety means for the electrophysiology cardiovascular catheter system having a tip electrode.